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Birds by name
22 July 2011
Image: Graham Catley
Swallow populations fluctuate from year to year and are affected greatly by weather.
They require rain for wet mud for nest building and for encouraging the abundance of insect prey. Cold periods and prolonged rain during the breeding season can, however, reduce the numbers of flying insects and lead to high levels of chick starvation.
Independent of weather-related fluctuations, there have been widespread declines in swallow numbers across Europe since 1970. The cause(s) of these declines is unknown but potential factors are discussed below.